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Summary of the Business and Significant Accounting Policies - Narrative (Details)
 12 Months Ended
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Dec. 31, 1986
Operating_Leases
Accounting Policies Disclosures [Line Items]        
Allowance for equity funds used during construction $ 10,430,000 $ 5,563,000 $ 4,382,000  
Weighted average borrowing rate 6.60% 6.60% 6.90%  
Interest costs incurred, capitalized $ 1,500,000 $ 1,600,000 $ 1,500,000  
Public Service Company of New Mexico [Member]        
Accounting Policies Disclosures [Line Items]        
Allowance for funds used during construction, capitalized interest 7,800,000 4,200,000 3,300,000  
Allowance for equity funds used during construction 10,430,000 5,563,000 4,382,000  
Interest costs incurred, capitalized 800,000 1,100,000 1,100,000  
Impairment losses on securities held in the NDT $ 10,400,000 4,800,000 3,500,000  
Public Service Company of New Mexico [Member] | 10.3% Lessor Notes [Member]        
Accounting Policies Disclosures [Line Items]        
Notes receivable, stated percentage rate 10.30%      
Public Service Company of New Mexico [Member] | 10.15% Lessor Notes [Member]        
Accounting Policies Disclosures [Line Items]        
Notes receivable, stated percentage rate 10.15%      
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member]        
Accounting Policies Disclosures [Line Items]        
Number of operating leases | Operating_Leases       11
Texas-New Mexico Power Company [Member]        
Accounting Policies Disclosures [Line Items]        
Allowance for funds used during construction, capitalized interest $ 500,000 500,000 400,000  
Allowance for equity funds used during construction 0 0 0  
Interest costs incurred, capitalized $ 100,000 $ 100,000 $ 0